linux-kernel - [PATCH 3.2 086/102] KVM: x86: Improve thread safety in pit

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Message-ID: <lsq.1414880883.592571871@decadent.org.uk>
Date:	Sat, 01 Nov 2014 22:28:03 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Andy Honig" <ahonig@...gle.com>,
	"Paolo Bonzini" <pbonzini@...hat.com>
Subject: [PATCH 3.2 086/102] KVM: x86: Improve thread safety in pit

3.2.64-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Honig <ahonig@...gle.com>

commit 2febc839133280d5a5e8e1179c94ea674489dae2 upstream.

There's a race condition in the PIT emulation code in KVM.  In
__kvm_migrate_pit_timer the pit_timer object is accessed without
synchronization.  If the race condition occurs at the wrong time this
can crash the host kernel.

This fixes CVE-2014-3611.

Signed-off-by: Andrew Honig <ahonig@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kvm/i8254.c | 2 ++
 1 file changed, 2 insertions(+)

--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -264,8 +264,10 @@ void __kvm_migrate_pit_timer(struct kvm_
 		return;
 
 	timer = &pit->pit_state.pit_timer.timer;
+	mutex_lock(&pit->pit_state.lock);
 	if (hrtimer_cancel(timer))
 		hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
+	mutex_unlock(&pit->pit_state.lock);
 }
 
 static void destroy_pit_timer(struct kvm_pit *pit)

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